The work proposed in this application concerns studies of synaptic regulation in the peripheral autonomic system of mammals, using the techniques of intracellular recording and electron microscopy. Based on results obtained so far, our major aims are (a) to determine the nature of the reversible synapse loss from sympathetic neurons that follows postganglionic axotomy; more specifically we are interested in whether the protein nerve growth factor plays a role in this effect; and (b) to understand the mechanism underlying the ability of preganglionic nerve cells to make preferential connections with different functional classes of ganglion cells. The significance of this line of investigation lies in understanding some of the general ways in which the formation and maintenance of synaptic connections are governed, an area likely to be of fundamental importance in the normal and pathological functioning of the mammalian nervous system.